I have a Dillon taper crimp die for .38 Super. It's nice, but won't do anything a polished Lee taper crimp die won't do. No, they do not come as polished as the Dillon. You have to do it yourself.
For auto calibers there is so little movement while applying a light taper crimp, that it is no problem seating and crimping at the same time.
For revolver rounds using lead bullets with a good crimp groove, seating and crimping in the same step works great.
For revolver rounds using jacketed bullets with a proper cannelure (A groove for the brass to crimp down in to), seating and crimping in the same step works just fine. With poor cannelures (No indention, just marks), seating and crimping in the same step can be problematic.